The present invention relates to driving equipment intended for synchronous motors; the invention relates more specifically to driving equipment that improves the output torque of a synchronous motor and enables highly efficient operation of the motor.
Various methods are proposed for the linearization of the output torque of a synchronous motor. Japanese Application Patent Laid-open Publication No. 2000-358400, for example, discloses a method in which the output torque can be linearized without providing sophisticated calculation operations on torque command values.
Various methods are also proposed for highly efficient control of a synchronous motor. To operate motors very efficiently, it is desirable that when motor currents of the same magnitude are applied, the resulting output torque should be utilized to their maximums. It is therefore considered that maximum torque per ampere control can be realized by converting the relationship of the maximum torque with respect to the motor currents to mathematical modeling or table form. Japanese Application Patent Laid-open Publication No. Hei 07-308088, for example, discloses a method in which the appropriate current amplitude command and current phase command can be calculated using the torque command and rotational speed of the motor as the parameters.
Highly efficient control cannot always be achieved using the method disclosed in Japanese Application Patent Laid-open Publication No. 2000-358400 mentioned above. In addition, in Japanese Application Patent Laid-open Publication No. Hei 07-308088 mentioned above, although a method of calculating current amplitude and current phase command values is described in which the function corresponding to the particular torque command value is to be stored in numeric expression form to memory each time the current amplitude command value and the current phase command value are to be calculated, more specific numeric expressions are not disclosed. Furthermore, in Japanese Application Patent Laid-open Publication No. Hei 07-308088 mentioned above, although a method of storing function patterns to memory and reading out the data each time is disclosed, this method has the disadvantage that the volume of data to be stored to memory tends to increase.
Because of its complexity, the relationship between the torque and current of a synchronous motor is not easy to formulate accurately. The use of complex calculation equations during the formulation increases the amount of calculation required and, hence, the calculation time, and requires an expensive microcomputer for control. For these reasons, it is desirable that when a function is to be stored as a numeric expression and then to be calculated each time, the calculation should be conducted using a calculation equation as simple as possible.
The present invention is intended to supply a method and equipment by which the output torque and speed control system of a synchronous motor can be linearized using an inexpensive microcomputer, instead of providing sophisticated calculation operations, and thus the motor can be controlled with high efficiency.
The driving equipment for synchronous motors that pertains to the present invention is equipped with
an inverter for converting a direct-current voltage to an alternating current or a direct current and supplying the current to a synchronous motor,
control apparatus for controlling the output voltage and frequency of the inverter, and
a means for detecting or estimating the rotational speed of said synchronous motor,
wherein said control apparatus is further equipped with a means for issuing such a torque command that matches said rotational speed and a rotational speed command, and a means for first receiving said torque command as an input signal, then computing current amplitude and current phase data, and sending the data as an output signal, and in addition, there is provided a maximum torque/current ratio control means by which the relationships between the maximum torque and the current amplitude and between the maximum torque and the current phase are converted to numeric expressions having the torque represented by a parameterized function, and current amplitude command and current phase command data with which the maximum torque can be obtained with respect to the entered torque command is computed and transmitted as output data. In the driving equipment for synchronous motors that pertains to the present invention, the parameterized function denoting the above-mentioned torque acts as a linear function or a quadratic function.
The driving equipment for synchronous reluctance motors that pertains to the present invention is equipped with a maximum torque/current ratio control means by which the relationships between the maximum torque and the current amplitude and between the maximum torque and the current phase are converted to numeric expressions having the torque represented by a parameterized function, and current amplitude command and current phase command data with which the maximum torque can be obtained with respect to the entered torque command is computed and transmitted as output data, and the parameterized function denoting the above-mentioned torque acts as a linear function or a quadratic function.